Pneumonic plague protection induced by a monophosphoryl lipid A decorated Yersinia outer-membrane-vesicle vaccine

A newly constructed Yersinia pseudotuberculosis mutant (YptbS46) carrying the lpxE insertion and pmrF-J deletion exclusively synthesized an adjuvant form of lipid A, monophosphoryl lipid A (MPLA). Outer membrane vesicles (OMVs) isolated from YptbS46 harboring an lcrV expression plasmid, pSMV13, were designated OMV46-LcrV, which contained MPLA and high amounts of LcrV and displayed low activation of Toll-like receptor 4 (TLR4). Similar to the previous OMV44-LcrV, intramuscular prime-boost immunization with 30 {micro}g of OMV46-LcrV exhibited substantially reduced reactogenicity and conferred complete protection to mice against a high-dose of respiratory Y. pestis challenge. OMV46-LcrV immunization induced robust adaptive responses in both lung mucosal and systemic compartments and orchestrated innate immunity in the lung, which were correlated with rapid bacterial clearance and unremarkable lung damage during Y. pestis challenge. Additionally, OMV46-LcrV immunization conferred long-term protection. Moreover, immunization with reduced doses of OMV46-LcrV exhibited further lower reactogenicity and still provided great protection against pneumonic plague. Our studies strongly demonstrate the feasibility of OMV46-LcrV as a new type of plague vaccine candidate.